1. Field of the Invention
An object of the present invention is a device for the transmission of a decoy signal. It also relates to a method for the transmission of a decoy signal. It can be applied in the field of mobile telephony, especially to mobile telephones working according to a standard or specification for which a CDMA type access protocol is envisaged. Standards or specifications using such protocols include the IS95 standard or the IMT2000 standard or more particularly the UMTS standard. More generally, the invention can be applied in transmission/reception systems for which, in a synchronization phase, measurements are made of a power value of a received signal. These measurements of power values are used to select the most powerful encoded signal from among all the encoded signals received, an encoded signal being obtained through the use of a spread-spectrum technology. The aim of the invention is to make a device for the transmission of a decoy signal, thus simulating the presence of a base station in a limited geographical zone with which a mobile telephone gets connected, the mobile telephone being within a limited geographical zone. The aim of the invention also relates to a method for the transmission of a decoy signal that is implemented especially in the device of the invention.
2. Description of the Prior Art
At the present time, the deployment of a mobile telephony network, especially in a town, enables a mobile telephone to get connected to this network from almost any place whatsoever. Thus, a user can freely access a mobile telephony network through a mobile telephone, but it is also possible to contact this user in any place whatsoever.
This free access from any place whatsoever raises problems. Indeed, there are places where silence is necessary depending on the activities being performed in this place. This is especially so in places of entertainment where any sound, other than that produced by the show itself, is considered to be an acoustic nuisance. These entertainment halls are generally cinema halls, opera halls, concert halls or again auditoriums. This may also be the case in conference rooms, lecture rooms and lecture halls. An acoustic nuisance in a place of this kind usually results from the ringing of a mobile telephone. Thus, a mobile telephone that rings in a place like this disturbs an established ambience by creating an acoustic nuisance.
There are known ways of sending a decoy signal to a mobile telephone so that it does not ring in public places such as this. However, in these known applications, a call is set up according to a protocol between a mobile telephone and a base station. This call is often complicated and difficult to implement because the base station has to send special messages which must be acknowledged or not acknowledged by the mobile telephone. Furthermore, the mobile telephone has to be modified so that it can interpret this protocol in order to find out whether or not it is in a place of this kind.
It is an object of the present invention to overcome these problems of acoustic nuisance by proposing a device for the transmission of a decoy signal used as a synchronization signal by a mobile telephone which is in a place to be protected against acoustic nuisance from a mobile telephone. In the invention, a mobile telephone, in a zone to be protected against an acoustic nuisance, will get connected with a device for the transmission of a decoy signal. Thus, a fictitious base station is created. This fictitious base station has certain elementary characteristics of a real base station with which the mobile telephones, which are present in the limited geographical zone, will get connected.
Furthermore, the device and the method of the invention use prior art mobile telephones that work according to a CDMA type access protocol. With this type of access protocol, a connection phase with a base station consists, inter alia, of a measurement of power of a received signal. The mobile telephone gets connected with the base station that sends the signal whose power, at reception by the mobile telephone, is the highest possible power.
The present invention therefore relates to a method for the transmission of a decoy signal, which is a radioelectric mobile telephony signal according to a CDMA type access protocol, in a limited geographical zone, wherein:
a measurement is made, by means of a dummy receiver, in the limited geographical zone, of the power of one or more synchronization signals received in this limited geographical zone and transmitted by base stations of a mobile telephony network,
a candidate signal is chosen from among the synchronization signals received for which the power value is the greatest in the limited geographical zone,
the receiver is temporally synchronized with the received signal,
a decoy signal that is the replica of the chosen signal is produced,
the decoy signal is amplified up to a power value that is strictly greater than a power value of the chosen signal,
the decoy signal is sent inside the limited geographical zone by means of a dummy transmitter, the decoy signal being temporally desynchronized with respect to the chosen signal and the other candidate radioelectric signals,
a mobile telephone is radioelectrically connected with the dummy transmitter, the mobile telephone being inside the limited geographical zone.
The invention also relates to a device for the transmission of a mobile telephony radioelectric decoy signal in a limited geographical zone comprising a dummy receiver and a dummy transmitter sending a signal that is desynchronized with respect to the signal received by the dummy receiver and is more powerful than this received signal.